In the past 2 decades, there has been considerable interest in aliphatic polycarbonates for widespread applications in medicine and pharmacy because of their high biocompatibility, facile biodegradation, low toxicity, and excellent mechanical properties.
The most convenient method for preparing polycarbonates with high molecular weights and narrow molecular weight distributions seems to be the ring-opening polymerization (ROP) of cyclic carbonates. However, ring-opening polymerization of five-membered cyclic carbonates like ethylene carbonate (EC) or propylene carbonate (PC) does not allow to obtain pure poly(ethylene carbonate) (PEC) and poly(propylene carbonate) (PPC) homopolymers. As such, during the last decades some groups have tried to copolymerize cyclic carbonates with cyclic esters.
It is very difficult for five-membered cyclic carbonates to co-polymerize, or to ring-open without undergoing undesirable decarboxylation side reactions, or to react without degradation, or without producing un-recoverable copolymers, only to name a few of the problems involved. In addition, the selection of the catalyst can be critical. Catalytic systems based on tin, aluminum, rare earth metals, magnesium or calcium are known as catalysts for the ring-opening polymerization of cyclic carbonates. However, some of these catalysts are possibly toxic or at least possibly involve toxic reagents during the polymerization process, which makes these unsuitable for producing pharmaceutical grade aliphatic polycarbonates. Also, some of these catalysts are very sensitive to protic impurities and are not well suited for large scale industrial applications.
There is therefore a need for improved and effectively workable processes of copolymerization of cyclic carbonates.
Consequently, it is an object of the present invention to provide an improved process for the effective copolymerization of ethylene carbonate It is also an objective of the present invention to prepare fully bio resourced polycarbonate/polyester copolymer